One possible plot could be that due to some magical anomaly, Fairy Tail is transported to Lucy's location much earlier than in the original story. She witnesses their power and heroics first - hand and is so inspired that she asks to join right away. This early joining would also mean she gets to participate in different quests and build relationships with the members much sooner. This could lead to stronger bonds with characters like Erza, Gray, and Happy, as they would be part of her earlier adventures in the guild.
In this fanfiction, perhaps Lucy joins Fairy Tail right after she discovers her magic abilities. This would change a lot of the initial interactions. She could be more naive and inexperienced when joining, which would lead to different dynamics within the guild. Like, she might be more reliant on the others for guidance in using her magic, rather than having some basic skills already when she actually joins in the original story.
Erza would be one of the main characters affected. In the original story, when Lucy joins, Erza has a certain perception of her. But if Lucy joins earlier, Erza might see her as a more inexperienced mage and take her under her wing even more. Gray might also have different interactions with Lucy. He could be more of a mentor figure to her in the beginning, teaching her about controlling her magic in cold environments, which is something he's good at.
Well, one possibility is that Natsu could join Fairy Tail in a different way than in the original story. Maybe he has some special mission before officially becoming a member. For example, he has to prove his loyalty by helping an elder member with a personal problem.
One possible plot could be that Acnologia, with his immense power, initially causes chaos within Fairy Tail. The members are both in awe and afraid of him. But as time passes, he starts to understand the concept of friendship and loyalty in Fairy Tail. He could then use his power to protect the guild from other major threats, like the Alvarez Empire. This would completely change the power dynamics in the Fairy Tail world.
The plot might revolve around Yukino's journey of self - discovery within Fairy Tail. At first, she might feel like an outsider, but as she gets involved in the guild's daily activities, she starts to find her true self. For example, she could participate in the Grand Magic Games as a representative of Fairy Tail. During the games, she showcases her skills and also learns about the value of teamwork and friendship within the guild.
The plot could involve Kagome bringing her spiritual powers and archery skills to Fairy Tail. Maybe she'd form a team with some of the guild's mages and go on adventures. She could use her holy powers to combat dark magic threats in the Fairy Tail world.
If Lucy never joined Fairy Tail, the friendships and relationships among the characters would form in a very different way. Also, many of the story arcs might not unfold as they do in the original plot.
One possible plot could be that Igneel's arrival in Fairy Tail brings a new level of power and protection. He could start training the mages in new and powerful dragon - slaying magic, making Fairy Tail even more formidable against their enemies.
One possible plot could be Sasuke initially being a bit of an outcast in Fairy Tail because of his brooding nature. But as he goes on quests with the guild members, he starts to open up. For example, he might team up with Natsu for a mission where they have to fight a powerful dark wizard. Through their battles and interactions, Sasuke learns about the power of friendship in Fairy Tail, which is very different from his past experiences in Naruto's world.
One possible plot twist could be that Zeref has an ulterior motive for joining. Maybe he wants to use the guild's resources to further his own dark plans.
Well, the plot could involve Kakashi bringing his ninja skills to the Fairy Tail guild. He might teach the wizards some unique combat techniques from the ninja world. For example, his Chidori could be adapted into a magic spell in the Fairy Tail universe. Maybe he'd form a team with Natsu and Lucy, and they'd go on adventures together, with Kakashi's strategic mind helping them out in tough battles against dark guilds.